Mystery solved!

Being the lazy person that I am, one of the first things I do after installing Firefox is to set up keyword search. This way, I can just type in whatever in the URL bar and out comes the result page in my chosen web services.

Being the poor person that I am, I use AVG for anti-virus. Not long ago, it popped up with a reminder that the then current version will not be updated after certain days and urged me to upgrade to the next version 8.0, which I did.

I haven't been playing around much in Firefox lately and mostly just used the bookmark to go to selected sites. I used the URL bar to search occasionally but those were all in English.

That's why I didn't notice the problem until today, when I tried to search 'Kagamine Rin' 'kokoro' 'kiseki' in Japanese. As soon as I typed in the terms, the "xxx has encountered a problem and needs to close" message jumped at me. All my attempts ended with the same error message and the Talk Back agent window. Time to troubleshoot.

It didn't happen when I search via Ctrl+K, only when I used the URL bar. I tried English, no problem. I tried Japanese, crashed. I tried Chinese, crashed. I went into about:config, nothing wrong. I tried rebooting the computer, same thing. I tried Mozilla Suite, no problem.

Then it dawned on me. During the few times that I searched this past week, I remember vaguely that there's some kind of green mark beside the search results, an indication that the link is deemed safe by AVG. I thought it might be the security toolbar I agreed to install at the time of upgrade. Not seeing an option to uninstall the toolbar by itself, I uninstalled the whole thing and reinstalled it minus the toolbar. Same thing.

I was at my wit's end and was considering switching to a different anti-virus software. As a last effort, I opened the suspect and tried to see if I can find a setting for it. Then my eyes landed on the LinkScanner icon. I clicked on it once. Nothing. I right-clicked on it. Nothing. I finally double clicked on it and got the option to appear. There's no mouse over description as well. Not too friendly to an UI dummy like me... -__-

Anyway, my keyword search is now back to normal after I disabled the LinkScanner. I'm so happy...（つД`）

Lessons for the day are
1) It can be a pain and sometimes downright frustrating to use non-English characters in an English software environment. It shouldn't be like this, especially considering that Windows XP (and I assume Vista as well?) is UTF-8.
2) Make your UI more friendly for people like me please!! I could have resolved the problem with a few mouse clicks and saved the time I wasted uninstalling and reinstalling and rebooting
3) Don't install all features by default! If you offer a customized route during installation, makes all features beside the core component (in this case the anti-virus part) available for choosing. And have clear descriptions for the features and let the user decides. I wouldn't had enabled the LinkScanner if I had the choice.
4) Stop ranting on and on and making the post so long...